The driving of processing machines, tools and the like by means of electromotors depends as far as the rotational speed and the torque are concerned on the type of motor and on the electric supply network. However, as a variable speed may be advantageous in many employments frequency converters may be inserted.
The known static frequency converters are bulky devices to be externally installed, and the structural dimensions of these devices depend on the necessary transmission of heat to the ambient. It turned out that the frequency converter can be miniaturized by means of a highly-integrated switching network in such a manner that it can be situated adjacent to the motor or in or on, respectively, the unit driven by the motor. The latter as well as a small structural size are, however, caused by the dissipation of heat of the frequency converter being freely liberatable so as to avoid exceeding of the prescribed thermal limit of the electronics.
In connection with, for instance, pump assemblies or ventilators the speed and torque of which must be controlled or adjusted by means of frequency converters, it is possible to utilize the liquid delivered for lowering the heat. The latter implies that specific measures must be taken when building the frequency converter.